This invention relates to lamps having lead-in wires which are hermetically sealed through an end of the lamp envelope by pinching the envelope material to form a press-seal and, more particularly, to tungsten-halogen lamps having a tubular envelope of quartz or high silica glass with a press-seal at one end.
Such lamps are often employed in high wattage applications and include one or more tungsten filaments enclosed within a sealed envelope of quartz or high silica glass. The atmosphere within the envelope generally contains a halogen, such as iodine or bromine, whereby the lamp operates on a regenerative cycle initiated when a tungsten halide is produced and chemically combines with the particles evaporated from the incandescing tungsten filament. Subsequent thermal decomposition of this compound replaces the tunsten particles in the filament.
In the fabrication of these lamps, the important sealing operation includes using wafer-thin strips of molybdenum foil as current conductors in the seal area. These strips respectively are welded between outer lead-in wires and inner lead-in wires functioning as a filament support wires and assembled into a quartz of high silica glass tubular envelope; thereafter, an end portion of the envelope is softened, and a mechanical sealing die is utilized to form the seal. This sealing operation pinches the area where the molybdenum strip bridges the lead-in wires and provides a vacuum-tight seal, referred to as a press-seal. The width of this press-seal is at least as wide as the diameter of the tubular envelope and generally somewhat wider. Depending upon the die used in pinching this sealed area, the lower corners of the press-seal may define a semi-rectangular configuration, or the sides of the press-seal may be pinched out into a somewhat irregular contour.
Normally, in the basing of such lamps, especially the high wattage types, a ceramic base holder is utilized with prongs, buttons, or the like, for connection to the lead-in wires. Typically, the ceramic base is provided with a slot for receiving the press-sealed, single-ended lamp. The lamp is fitted and aligned into the slot in the ceramic base and secured therein by applying a basing cement completely around the press-seal of the lamp envelope.
In order to satisfy some lamp applications, it is necessary to provide a comparatively large glass envelope. The resulting end seal section of the envelope reserved for a base member may then be too large to fit existing basing means and holding devices. For example, whereas the application in which a given lamp is to be used may only accommodate a base designed for a T4 press-seal, the light output requirements may require the use of a larger T6 bulb. The press-seal of the T6 tubular envelope, however, would clearly not fit the smaller T4-adaptable base. One approach which has been employed to overcome this problem has been to use the comparatively non-standard G6 globular bulb which is manufactured by using a blown T4 tabulation at considerably higher cost as compared to conventional manufacturing processes. The non-uniform configuration of the globular bulb also requires special care to maintain bulb to exhaust tube alignment.